Interaction between local blood flow and tolerance to prolonged pain in the elderly.

PURPOSE: We aimed to explore the link between local vasodilation and pain perception in elderly subjects, testing the hypothesis that altered local cutaneous blood flow participates in the decrease in pain tolerance with age. METHOD: Sixty-eight young and 83 older participants performed a pain tolerance test in which they hold their hand in an airtight box in which air temperature was regulated at 65 °C until the pain became unbearable. Participants continuously estimated pain intensity. Skin temperature and local blood flow in the box-exposed hand were continuously monitored. RESULTS: In the young group, 97% of subjects resisted pain until the end of the test, whereas only 53% in the elderly group managed to do so, indicating that pain tolerance is impaired in the elderly. Among all participants, the skin temperature associated with the first pain sensation was below the threshold for nociceptor activation (43 °C). Interestingly, blood flow in the elderly group was correlated with pain judgment, whereas no such correlation was observed in the young. CONCLUSION: Our results suggest that the local vasodilator response induced by local heating may be involved in pain perception and may influence thermal pain tolerance with aging. These results could contribute to a better understanding of vascular deficits and the development of chronic pain in vascular pathologies.

Preserved distraction analgesia but greater impact of pain on task performance in older adults compared with younger subjects.

OBJECTIVE: In this study, we compared two working memory conditions to study the analgesic effect of a distraction in elderly vs young people and the effect of pain on performance on the distracting task. METHODS: Younger (n=27) and older (n= 34) subjects performed 1- and 2-Back working memory tasks, representing low and high cognitive loads, respectively. Infrequent, brief hot nociceptive and cold non-nociceptive stimulations were delivered 100 ms before visual N-Back stimuli. Contact heat-evoked and cold-evoked potentials (N2P2 component) were analyzed in the absence of cognitive tasks and during the N-Back tasks. We compared the pain and cold intensity ratings and reaction times in trials preceded by nociceptive and cold stimulations and in trials not preceded by thermal stimulations between groups and between N-Back conditions. RESULTS: In both groups, performing the 1- and 2-Back working memory tasks reduced the perceived intensity of nociceptive and cold stimuli. In elderly subjects performing 2-Back memory tasks, response times to trials after nociceptive stimulation were longer than those to trials after cold or non-stimulation. By contrast, thermal stimulations had no effect on reaction times in young subjects. The amplitude of the N2P2 component was lower in the older than in the younger group in the absence of a cognitive task. In the older group, N-Back tasks had no effect on the N2P2 amplitude, whereas they reduced N2P2 amplitude in the young. CONCLUSION: Distraction analgesia is preserved in elderly subjects. However, this successful pain modulation seems to be accompanied by performance costs in the distracting tasks.